1. Field of the Invention
The present invention relates to an image reading apparatus capable of reading both sides of a document, and an image forming apparatus provided with the image reading apparatus.
2. Description of the Related Art
Conventionally, in image forming apparatuses such as a copying machine and a facsimile machine, front and back sides of a document is automatically read by an image reading apparatus provided with an automatic document feeding device (ADF: Automatic Document Feeder). In this document reading, there has been widely adopted a method of reading an image on a front side of a document with an image sensor, reversing the document front and back, and then reading an image on a back side of the document again with the image sensor.
Japanese Patent Unexamined Publication No. 2004-15299 discloses an apparatus which is capable of setting any one of a double-sided simultaneous-reading mode and a double-sided reverse reading mode. In the double-sided simultaneous-reading mode, a minification optical system image sensor provided on a side of an apparatus main body reads one side of a document, and a contact-type optical system image sensor provided on a side of an automatic document feeding device reads the other side of the document, and the both sides of the document are read substantially simultaneously by one document conveyance (one-path) without reversing the document. In the double-sided reverse reading mode, a document read by the minification optical system image sensor is reversed and read again by the minification optical system image sensor.
However, according to the apparatus disclosed in Japanese Patent Unexamined Publication No. 2004-15299, in a case where the double-sided reverse reading mode is set, the document is reversed and a back side is read by the minification optical system image sensor even if the back side is blank, so that a problem of a time loss occurs. Further, at a time of reading a document stack successively, in a case where the document stack includes a large number of documents being blank on their back sides, the time loss becomes excessively large.